This invention relates to the measurement of variations in the velocity of wind at a specific location, such as the measurement of the velocity of gusts which may have a duration of a few seconds.
Conventional wind measurements are carried out by instruments, such as the cup anemometer, that respond in a time which is comparable to or shorter than the times of interest for variations or gusts in the wind. These variations can be resolved in time and measured directly. However, instruments of this type have to be physically mounted to the ground or a support structure and hence there are severe limitations on where the measurement can be made.
Another type of instrument provides for the measurement of average winds from a remote location. One such instrument is the doppler acoustic echo system shown in U.S. Pat. No. 3,889,533. A signal is transmitted from the ground to the location at which the measurement is to be made. This signal is scattered, and the scattered signal along two or more paths is picked up by antennas on the ground, giving a measure of components of the wind at various altitudes, up to several hundred meters for a typical instrument.
However, interfering noise in the acoustic echo system generally prevents a confident measurement from being made in a time interval of a few seconds. To compensate for the weak scattered signal relative to the noise, the received signals are averaged over a longer interval, typically 1 or 2 minutes or more, so that the noise can be smoothed and the scattered signal can be observed to provide a measure of the average wind velocity. The interval required for averaging is longer than some intervals of interest in measuring wind variability in the nature of gusts, which may have a duration of only a few seconds.
Accordingly, it is an object of the present invention to provide method and apparatus for measurement from a remote location of variations in velocity of wind, which variations may occur in a few seconds. Other objects, advantages, features and results will more fully appear in the course of the following description.